1. Field of the Invention
The present invention relates to an ultrasound diagnostic apparatus and ultrasound signal analyzing method which measure a blood flow velocity and the like and provide information effective for medical diagnosis.
2. Description of the Related Art
An ultrasound diagnostic apparatus is a medical image device which noninvasively obtains a tomographic image of soft tissue in a living body from the body surface by the ultrasound pulse reflecting method. This ultrasound diagnostic apparatus has advantages of being smaller in size, more inexpensive, and safer because of no exposure to X-rays and the like than other medical image devices, and of being capable of blood flow imaging, and hence is widely used in a cardiac department, abdominal department, urological department, obstetrics and gynecology, and the like.
This ultrasound diagnostic apparatus can provide not only an ultrasound image generated on the basis of an acquired echo signal but also clinical information obtained by quantitative analysis using the echo signal. Quantitative analysis includes a type associated with morphological information and a type associated with blood flow information. The latter type, in particular, typically uses blood flow indexes such as a PI (Pulsatility Index), RI (Resistance Index), S/D (Systelic Velocity/Diastoric Velocity), and the like calculated by using Doppler waveforms. For example, these blood flow indexes are acquired in the following manner.
First of all, a Doppler waveform acquired by a Doppler mode is displayed as shown in FIG. 1. An operator determines a display scale for a Doppler waveform by manually moving a baseline Lb indicating velocity 0 to an arbitrary position. When a display scale is determined, an automatic tracing process for extracting an approximate shape of the Doppler waveform in a predetermined direction (the positive direction of velocity in FIG. 2). Quantitative indexes for a blood flow such as a PI, RI, and S/D are calculated by using an approximate waveform Wa like that shown in FIG. 2 which is extracted in this manner.
In the conventional ultrasound diagnostic apparatus, a direction (tracing direction) in which an approximate waveform is to be extracted by an automatic tracing process must be artificially set before automatic tracing. If, therefore, the operator forgets to set a tracing direction, an automatic tracing process is executed in a previously or initially set tracing direction.